The invention relates to a tube, known as a straw, for cryogenically preserving biological samples, in particular viral cultures, formed by a length of tubular envelope made of biologically neutral, substantially transparent polymer material, provided with a seal at each of its two ends and including, in the vicinity of a first end, a sliding stopper comprising an aqueous gel between two pads made of porous elastic material.
The invention also relates to a process for filling a tube or straw of this type.